tokfandomcom-20200215-history
Archaic human migrations
(yellow), (ochre) and (red).}} Several expansions of populations of (genus ) out of Africa and throughout Eurasia took place in the course of the , and into the beginning , between about 2.1 million and 0.2 million years ago (Ma). These expansions are collectively known as Out of Africa I, in contrast to the expansion of ( ) into Eurasia, which may have begun shortly after 0.2 million years ago (known in this context as " "). The earliest presence of Homo (or indeed any ) outside of Africa dates to close to 2 million years ago. A 2018 study claims human presence at , central China, as early as 2.12 Ma based on of the lowest layer containing stone artefacts. The oldest known human skeletal remains outside of Africa are from , ( ), and are dated to 1.8 Ma. These remains are classified as . Later waves of expansion are proposed around 1.4 Ma (early industries), associated with and 0.8 Ma ( Acheulean groups, associated with ). Until the early 1980s, early humans were thought to have been restricted to the African continent in the , or until about 0.8 Ma; Hominin migrations outside East Africa were apparently rare in the Early Pleistocene, leaving a fragmentary record of events. Early dispersals }} Pre-''Homo'' hominin expansion out of Africa is suggested by the presence of and , found in Greece and Anatolia and dated to c. 8 million years ago, but these are probably but not Hominini. Possibly related are the found in Crete, dated to close to 6 million years ago. emerge about 5.6 million years ago, in East Africa ( ). ( ) emerge in the same region, around 4 million years ago. The earliest known retouched tools were found in , Kenya, and date back to 3.3 Ma, in the late . They might be the product of or , the two known hominins contemporary with the tools. is assumed to have emerged by around 2 million years ago, being found at about 2.1 million years ago at , . The delineation of the "human" genus, , from Australopithecus is somewhat contentious, for which reason the superordinate term "hominin" is often used to include both. "Hominin" technically includes as well as as old as 10 million years ago (the separation of into Hominini and ). The earliest known hominin presence outside of Africa, dates to close to 2 million years ago. A 2018 study claims evidence for human presence at , central China, as early as 2.12 Ma based on of the lowest layer containing stone artefacts. It has been suggested that was descended from such an early expansion. It is not clear whether these earliest hominins leaving Africa should be considered Homo habilis, or a form of early Homo or late Australopithecus closely related to Homo habilis, or a very early form of Homo erectus. In any case, the morphology of H. floresiensis has been found to show greatest similarity with , and , raising the possibility that the ancestors of H. floresiensis left Africa before the appearance of H. erectus. A published in 2017 suggests that H. floresiensis was descended from a species (presumably Australopithecine) ancestral to , making it a "sister species" either to H. habilis or to a minimally habilis-''erectus''-''ergaster''-''sapiens'' , and its line is older than H. erectus itself. On the basis of this classification, H. floresiensis is hypothesized to represent a hitherto unknown and very early migration out of Africa, dating to before 2.1 million years ago. A similar conclusion is suggested by the date of 2.1 Ma for the oldest artefacts. ''Homo erectus'' ) finds}} emerges just after 2 million years ago. Early H. erectus would have lived face to face with H. habilis in East Africa for nearly half a million years. The oldest Homo erectus fossils appear almost contemporaneously, shortly after two million years ago, both in Africa and in the Caucasus. The earliest well-dated Eurasian H. erectus site is in Georgia, securely dated to 1.8 Ma. A skull found at Dmanisi is evidence for caring for the old. The skull shows that this Homo erectus was advanced in age and had lost all but one tooth years before death, and it is perhaps unlikely that this hominid would have survived alone. It is not certain, however, that this is sufficient proof for caring – a partially paralysed chimpanzee at the Gombe reserve survived for years without help. The earliest known evidence for African H. erectus, dubbed , is a single occipital bone (KNM-ER 2598), described as "H. erectus-like", and dated to about 1.9 Ma (contemporary with ). This is followed by a fossil gap, the next available fossil being , a skull dated to 1.6 Ma. sites in North Africa, the geographical intermediate of East Africa and Georgia, are in poor stratigraphic context. The earliest of the dated is in northern (c. 1.8 – 1.2 Ma), an layer. These sites attest that early Homo erectus have crossed the North African tracts, which are usually hot and dry. There is little time between Homo erectus’ apparent arrival in around 1.8 Ma, and its probable arrival in East and Southeast Asia. There is evidence of H. erectus in , China, dating to 1.7 Ma and in , on , Indonesia, from 1.66 Ma. Ferring et al. (2011) suggest that it was still that reached West Asia, and that early H. erectus developed there. H. erectus would then have dispersed from West Asia, to East Asia ( ) Southeast Asia ( ), back to Africa ( ), and to Europe ( ). It appears H. erectus took longer to move into Europe, the earliest site being in southeastern dated to 1.4 Ma, associated with , and a controversial in Southern Italy, allegedly from 1.7 – 1.3 Ma. The paleobiogeography of early human dispersals in western Eurasia characterizes H''. ex gr. ''erectus as a temperature sensitive , that failed to disperse north of the . The geographically restricted earliest human presence in the should be regarded as evidence of a sustainable presence of human population in this isolated area. The , situated south-west of the , was apparently characterized by a comparatively warm climate similar to that of the , while the climate of the western European area was mitigated by influence and could support the episodic hominin dispersals toward the . Apparently, the faunal exchanges between southeastern Europe and the Near East and southern Asia were controlled by the complex interaction of such geographic obstacles as the and the Strait, the climate barrier from the north of the range, and the 41 kyr glacial that repeatedly closed the Bosporus and thus triggered the two-way faunal exchange between and the , and, apparently, the further westward dispersal of the archaic hominins in Eurasia. By 1 Ma, Homo erectus had spread across Eurasia (mostly restricted to latitudes south of the ). It is hard to say, however, whether settlement was continuous in Western Europe, or if successive waves repopulated the territory in glacial interludes. Early tools at from 1.4 Ma is some evidence for a continuous settlement in the West, as successive waves out of Africa after then would likely have brought Acheulean technology to Western Europe. The presence of human remains in is good evidence for seafaring by Homo erectus late in the . Bednarik suggests that navigation had appeared by 1 Ma, possibly to exploit offshore fishing grounds. He has reproduced a primitive dirigible (steerable) raft to demonstrate the feasibility of faring across the on such a device, which he believes to have been done before 850 ka. The strait has maintained a width of at least 20 km for the whole of the Pleistocene. Such an achievement by Homo erectus in the Early Pleistocene offers some strength to the suggested water routes out of Africa, as the , , and exit routes are harder to consider if watercraft are deemed beyond the capacities of Homo erectus. ''Homo heidelbergensis'' .}} Archaic humans in Europe beginning about 0.8 Ma ( Acheulean groups) are classified as a separate, erectus-derived species, known as . H. heidelbergensis from about 0.4 Ma develops its own characteristic industry, known as . H. heidelbergensis is closely related to (also identified as Homo heidelbergensis sensu lato or African H. heidelbergensis), known to be present in southern Africa by 0.3 Ma. emerges before about 0.3 Ma from a lineage closely related to early H. heidelbergensis. The earliest presence of H. sapiens in West Asia, and thus the beginning of " ", may date to as early as 0.3 Ma and is ascertained for 0.13 Ma. Routes out of Africa Most attention as to the route taken from Africa to West Asia is given to the , connecting the Horn of Africa and Arabia, which may have allowed dry passage during some periods of the Pleistocene. Other candidates are and the . A route across the was suggested in the 1970s but is now considered unlikely. is a 30 km strait between East Africa and the Arabian Peninsula, with a small island, , 3 km off the Arabian bank. The strait has a major appeal in the study of Eurasian expansion in that it brings East Africa in direct proximity with Eurasia. It does not require hopping from one water body to the next across the North African desert. The land connection with Arabia disappeared in the Pliocene, and though it may have briefly reformed, the evaporation of the Red Sea and associated increase in salinity would have left traces in the fossil record after just 200 years and deposits after 600 years. Neither have been detected. A strong current flows from the Red Sea into the Indian Ocean and crossing would have been difficult without a land connection. Oldowan grade tools are reported from Perim Island, implying that the strait could have been crossed in the Early Pleistocene, but these finds have yet to be confirmed. The is the Atlantic entryway to the Mediterranean, where Spanish and Moroccan banks are only 14 km apart. A decrease in in the Pleistocene due to would not have brought this down to less than 10 km. Deep currents push westwards, and surface water flows strongly back into the Mediterranean. Entrance into Eurasia across the strait of Gibraltar could explain the hominin remains at Barranco León in southeastern Spain (1.4 Ma) and in northern Spain (1.2 Ma). But the site of Pirro Nord in southern Italy, allegedly from 1.3 – 1.7 Ma, suggests a possible arrival from the East. Resolution is insufficient to settle the matter. Passage across the was suggested by (1975) based on the 1973 discovery Sicilian Oldowan grade tools in Sicily. Radiometric dates, however, have not been produced, and the artefacts might as well be from the Middle Pleistocene, and it is unlikely that there was a land bridge during the Pleistocene. Causes for dispersal Climate change and hominin flexibility For a given species in a given environment, available resources will limit the number of individuals that can survive indefinitely. This is the . Upon reaching this threshold, individuals may find it easier to gather resources in the poorer yet less exploited peripheral environment than in the preferred habitat. Homo habilis could have developed some baseline behavioural flexibility prior to its expansion into the peripheries (such as encroaching into the predatory guild). This flexibility could then have been positively selected and amplified, leading to Homo erectus adaptation to the peripheral open habitats. A new and environmentally flexible hominin population could have come back to the old niche and replaced the ancestral population. Moreover, some step-wise shrinking of the woodland and the associated reduction of hominin carrying capacity in the woods around 1.8 Ma, 1.2 Ma, and 0.6 Ma would have stressed the carrying capacity's pressure for adapting to the . With Homo erectus new environmental flexibility, favourable climate fluxes likely opened it the way to the Levantine corridor, perhaps sporadically, in the Early Pleistocene. Chasing fauna implies that Oldowan hominins were not predators. However, Homo erectus appears to have followed animal migrations to the north during wetter periods, likely as a source of scavenged food. The sabre-tooth cat was an apex predator of the Early and Middle Pleistocene (before 12). It became extinct in Africa c. 1.5 Ma, but had already moved out through the Sinai, and is among the faunal remains of the ine hominin site of , c. 1.4 Ma. It could not break and its kills were likely an important food source for hominins, especially in glacial periods. In colder Eurasian times, the hominin diet would have to be principally meat-based and Acheulean hunters must have competed with cats. Coevolved zoonotic diseases and Belfer-Cohen suggest that the success of hominins within Eurasia once out of Africa is in part due to the absence of outside their original habitat. Zoonotic diseases are those that are transmitted from animals to humans. While a disease specific to hominins must keep its human host alive long enough to transmit itself, zoonotic diseases will not necessarily do so as they can complete their life cycle without humans. Still, these infections are well accustomed to human presence, having evolved alongside them. The higher an African ape's population density, the better a disease fares. 55% of chimps at the die of disease, most of them zoonotic. The majority of these diseases are still restricted to hot and damp African environments. Once hominins had moved out into drier and colder habitats of higher latitudes, one major limiting factor in population growth was out of the equation. Physiological traits While Homo habilis was certainly bipedal, its long arms are indicative of an arboreal adaptation. Homo erectus had longer legs and shorter arms, revealing a transition to obligate terrestriality, though it remains unclear how this change in relative leg length might have been an advantage. Sheer body size, on the other hand, seems to have allowed for better walking and . A larger Homo erectus would also more slowly and could thus cover greater distances before facing limitations. The ability for prolonged walking at a normal pace would have been a decisive factor for effective colonisation of Eurasia. References Category:Human evolution